SYSTEM FOR TREATING NOx-CONTAINING GAS STREAMS

ABSTRACT

In one embodiment, a system for treating a gas stream comprising NOx generated from an acid pickling solution includes a first chamber and a second chamber. The first chamber includes a first inlet communicating with a source of a gas comprising NOx, a second inlet communicating with a source of ozone, and an interior volume adapted to contact the gas comprising NOx introduced through the first inlet with the ozone introduced through the second inlet. The second chamber directly fluidly communicates with the first chamber and receives gaseous effluent comprising nitric acid from the first chamber. The second chamber includes a third inlet communicating with a source of water vapor, an interior volume adapted to contact the gaseous effluent from the first chamber with the water vapor, thereby solubilizing nitric acid in the gaseous effluent with the water vapor to provide a solubilized nitric acid, and an outlet for collecting solubilized nitric acid from the interior volume of the second chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority under35 U.S.C. §120 to, co-pending U.S. patent application Ser. No.13/027,312, filed on Feb. 15, 2011, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure is directed to methods and systems for treatinggases comprising NO_(x).

BACKGROUND

Many manufacturing treatment and combustion processes produce gases thatinclude gaseous nitrogen oxides (NO_(x)) and other undesirable gaseousproducts. For example, processes for acid pickling stainless steels andother alloys, which typically involve immersing the alloys for a time ina bath of a strongly acidic solution including nitric acid, result ingases above the bath that include NO_(x). Federal and localenvironmental laws may limit the content of NO_(x) that is dischargedinto the atmosphere. In the past decades, manufacturing companies haveundertaken considerable efforts to reduce the amount of NO_(x)discharged into the atmosphere.

One known method of removing NO_(x) from a gas stream includescontacting the gas stream with ozone to thereby oxidize the NO_(x) inthe gas stream and form oxidation products such as nitrogen sesquioxideand nitrogen pentoxide. The oxidation products produced by the ozonetreatment may be collected using aqueous scrubbers, for example, storedon-site, and discarded as a liquid waste stream. Discarding the liquidwaste material may require third-party waste collection and disposalservices.

It would be advantageous to provide an alternative method for removingNO_(x) from the gases produced in an alloy pickling process or othermanufacturing treatment or combustion process that results in a reducedamount of waste. More generally, it would be advantageous to provide amethod for removing NO_(x) from a gas stream produced in any process andthat results in a reduced amount of waste.

SUMMARY

One aspect according to the present disclosure is directed to methodsfor treating a gas stream comprising NO_(x). The methods includecontacting a gas stream comprising NO_(x) with ozone to thereby formoxidation products including nitrogen sesquioxide and nitrogenpentoxide. The methods further comprise reacting at least a portion ofthe nitrogen sesquioxide and nitrogen pentoxide with water to therebyform nitric acid, and recovering at least a portion of the nitric acid.

An additional aspect according to the present disclosure is directed tomethods for treating a gas stream comprising NO_(x), wherein the gasstream is produced in a process for pickling an alloy includingcontacting the alloy with an acidic solution comprising nitric acid. Forexample, the pickling process may comprise at least one of immersing thealloy in an acidic solution or spraying an acidic solution on the alloy.The methods comprise contacting the gas stream comprising NO_(x) withozone to thereby form oxidation products including nitrogen sesquioxideand nitrogen pentoxide. The methods further comprise reacting at least aportion of the nitrogen sesquioxide and nitrogen pentoxide with water tothereby form nitric acid, and recovering at least a portion of thenitric acid. In certain embodiments, at least a portion of the recoverednitric acid may be recycled back to the acidic solution used in thepickling treatment.

A further aspect according to the present disclosure is directed systemsfor treating a gas stream comprising NO_(x). The systems comprise afirst chamber and a second chamber. The first chamber includes a firstinlet communicating with a source of a gas comprising NO_(x), and asecond inlet communicating with a source of ozone. The first chamberalso includes an interior volume adapted to contact the gas comprisingNO_(x) gas with ozone, thereby producing intermediate products includingnitrogen sesquioxide and nitrogen pentoxide. At least of portion of thenitrogen sesquioxide and nitrogen pentoxide react within the firstchamber with water to form nitric acid. The second chamber receivesgases from the first chamber. The second chamber includes a third inletcommunicating with a source of water vapor and an interior volumeadapted to contact gases from the first chamber with water vapor,thereby solubilizing nitric acid in the gases in the water vapor. Thesecond chamber further includes an outlet for recovering at least aportion of the solubilized nitric acid.

In one particular embodiment of a system for treating a gas streamcomprising NO_(x) according to the present disclosure, the system isassociated with an acid pickling apparatus for pickling an alloy. Gasesincluding NO_(x) produced by the acid pickling apparatus may be treatedusing the system so as to recover nitric acid. Optionally, at least aportion of the recovered nitric acid is recycled to the acid picklingapparatus.

It is understood that the invention disclosed and described herein isnot limited to the embodiments disclosed in this Summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of various non-limiting embodiments disclosed anddescribed herein may be better understood by reference to theaccompanying figures, in which:

FIG. 1 is a flow diagram showing certain steps of a non-limitingembodiment of a method for treating a gas stream comprising NO_(x) gasaccording to the present disclosure; and

FIG. 2 is a schematic representation of a non-limiting embodiment of asystem for treating a gas stream comprising NO_(x) gas according to thepresent disclosure.

The reader will appreciate the foregoing details, as well as others,upon considering the following detailed description of certainnon-limiting embodiments according to the present disclosure. The readermay also comprehend additional details upon implementing or usingembodiments described herein.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

It is to be understood that the descriptions of the disclosednon-limiting embodiments herein may have been simplified to illustrateonly those features and characteristics that are relevant to a clearunderstanding of the disclosed embodiments, while eliminating, forpurposes of clarity, other features and characteristics. Persons havingordinary skill in the art, upon considering this description of thedisclosed embodiments, will recognize that other features andcharacteristics may be desirable in a particular implementation orapplication of the disclosed embodiments. However, because such otherfeatures and characteristics may be readily ascertained and implementedby persons having ordinary skill in the art upon considering thisdescription of the disclosed embodiments, and are, therefore, notnecessary for a complete understanding of the disclosed embodiments, adescription of such features, characteristics, and the like, is notprovided herein. As such, it is to be understood that the descriptionset forth herein is merely exemplary and illustrative of the disclosedembodiments and is not intended to limit the scope of the inventiondefined by the claims.

In the present disclosure, other than where otherwise indicated, allnumerical parameters are to be understood as being prefaced and modifiedin all instances by the term “about”, in which the numerical parameterspossess the inherent variability characteristic of the underlyingmeasurement techniques used to determine the numerical value of theparameter. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter described in the present description should atleast be construed in light of the number of reported significant digitsand by applying ordinary rounding techniques.

Also, any numerical range recited herein is intended to include allsub-ranges subsumed within the recited range. For example, a range of “1to 10” is intended to include all sub-ranges between (and including) therecited minimum value of 1 and the recited maximum value of 10, that is,having a minimum value equal to or greater than 1 and a maximum valueequal to or less than 10. Any maximum numerical limitation recitedherein is intended to include all lower numerical limitations subsumedtherein and any minimum numerical limitation recited herein is intendedto include all higher numerical limitations subsumed therein.Accordingly, Applicant reserves the right to amend the presentdisclosure, including the claims, to expressly recite any sub-rangessubsumed within the ranges expressly recited herein. All such ranges areintended to be inherently disclosed herein such that amending toexpressly recite any such sub-ranges would comply with the requirementsof 35 U.S.C. §112, first paragraph, and 35 U.S.C. §132(a).

The grammatical articles “one”, “a”, “an”, and “the”, as used herein,are intended to include “at least one” or “one or more”, unlessotherwise indicated. Thus, the articles are used herein to refer to oneor more than one (i.e., to “at least one”) of the grammatical objects ofthe article. By way of example, “a component” means one or morecomponents, and thus, possibly, more than one component is contemplatedand may be employed or used in an implementation of the describedembodiments. Further, the use of a singular noun includes the plural,and the use of a plural noun includes the singular, unless the contextof the usage indicates otherwise.

Any patent, publication, or other disclosure material that is said to beincorporated by reference herein, is incorporated herein in its entiretyunless otherwise indicated, but only to the extent that the incorporatedmaterial does not conflict with existing definitions, statements, orother disclosure material expressly set forth in this description. Assuch, and to the extent necessary, the express disclosure as set forthherein supersedes any conflicting material incorporated by referenceherein.

Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein is onlyincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material. Applicantreserves the right to amend the present disclosure to expressly reciteany subject matter, or portion thereof, incorporated by referenceherein.

The present disclosure includes descriptions of various embodiments. Itis to be understood that the various embodiments described herein areexemplary, illustrative, and non-limiting. Thus, the present disclosureis not limited by the description of the embodiments. Rather, theinvention is defined by the claims, which may be amended to recite anyfeatures or characteristics expressly or inherently described in orotherwise expressly or inherently supported by the present disclosure.Further, Applicant reserves the right to amend the claims toaffirmatively disclaim features or characteristics that may be presentin the prior art, but not necessarily expressly described herein.Therefore, any such amendments would comply with the requirements of 35U.S.C. §112, first paragraph, and 35 U.S.C. §132(a). The variousembodiments disclosed and described herein can comprise, consist of, orconsist essentially of the features and characteristics as variouslydescribed herein.

Various embodiments disclosed herein are directed to methods of treatinga gas stream comprising NO_(x). Such embodiments include contacting agas stream comprising NO_(x) gas with ozone, thereby forming oxidationproducts including nitrogen sesquioxide and nitrogen pentoxide. At leasta potion of the nitrogen sesquioxide and nitrogen pentoxide reactionproducts are reacted with water to form nitric acid, and at least aportion of the nitric acid is recovered and optionally may be applied insome useful purpose. Thus, in contrast to conventional methods fortreating NO_(x)-containing gases, all or a portion of the oxidationproducts resulting from the reaction of the NO_(x)containing gas withozone are not directly removed as a waste stream using an aqueousscrubber. Instead, water is reacted with at least a portion of thenitrogen sesquioxide and nitrogen pentoxide oxidation products to formnitric acid, and at least a portion of the nitric acid is recovered andmay be recycled or otherwise utilized. The nitric acid used in picklingof stainless steel and other alloys, for example, is expensive andrecycling at least a portion of the acid may significantly reduce costsassociated with pickling, as well as reduce the amount of waste fluidsproduced when the NO_(x)-containing gases generated by the picklingprocess are treated.

Embodiments of methods according to the present disclosure may befurther understood by reference to the flow diagram of FIG. 1. In afirst step, gaseous NO_(x), which may be part of a gas stream, and ozoneare reacted to produce oxidation products. The oxidation products mayinclude nitrogen sesquioxide (N₂O₃) and nitrogen pentoxide (N₂O₅). In asecond step, which may occur simultaneous with and/or removed in timefrom the first step, at least a portion of the nitrogen sesquioxide andnitrogen pentoxide react with water to form nitric acid (HNO₃). In athird step, at least a portion of the nitric acid is recovered.

Various embodiments disclosed herein are directed to systems fortreating a gas stream comprising NO_(x) with ozone and producing andrecovering nitric acid. One such embodiment is schematically depicted inFIG. 2, wherein system 13 includes a first chamber 1, a second chamber2, and, optionally, a third chamber 3. The chambers 1,2,3 may be regionsof an apparatus that communicate along a flow pathway. Alternatively,one or more of the chambers 1,2,3 may be separate structures thatcommunicate along a flow pathway.

The first chamber 1 of system 13 receives an NOx-containing gas streamand a gas stream including or consisting of ozone gas and is adapted tomix the streams together. First chamber 1 may include at least a firstinlet 4 and a second inlet 5, and includes an interior volume. Incertain non-limiting embodiments, the first chamber 1 may have adiameter of at least 24 inches. In certain non-limiting embodiments, thefirst chamber 1 may be at least 200 feet long. However, it will beunderstood that the first chamber 1 may have any dimensions and designsuitable for mixing together the NOx-containing gas stream and thestream including ozone and thereby facilitating reaction between the NOxand the ozone. In certain non-limiting embodiments, the temperature inthe first chamber 1 may be less than 140° F. In certain non-limitingembodiments, the pressure in the first chamber 1 may be 10.5 watercolumn (inches) vacuum. In certain non-limiting embodiments, the flowrate through the first chamber 1 of the NOx-containing gas and the gasincluding ozone may be at least 500 cubic feet/min. It will beunderstood that the conditions within the first chamber 1 may beselected to facilitate reaction between the NOx-containing gas streamand the stream including ozone and the further reaction of materialsformed in the first chamber 1 to produce nitric acid. The flow ratewithin the first chamber 1 may be selected to permit adequate residencetime in the first chamber 1. If residence time within the first chamber1 is not adequate, the NOx-containing gas stream and ozone may havedifficulty mixing and reacting. In such case, oxidation products may notform in the first chamber 1, but instead might form in the secondchamber 2 or third chamber 3. In certain non-limiting embodiments, theresidence time in the first chamber 1 is at least 6 seconds.

The first inlet 4 communicates with a source of a gas including NO_(x).The NOx-containing gas stream preferably does not pass through ascrubber prior to passing through the first inlet 4 into the firstchamber 1. Instead, the NOx-containing gas stream preferably passesdirectly through the first inlet 4 from the source generating theNOx-containing gas stream and is not “pre-treated”. The NOx-containinggas stream may be generated from any process that produces NOx gases.For example, in certain non-limiting embodiments, the NOx-containing gasstream is generated during an alloy manufacturing or treatment processor a combustion process. In certain non-limiting embodiments,NOx-containing gas treated by a system according to the presentdisclosure is produced in a pickling process for treating metals andalloys. In one particular non-limiting embodiment, the NO_(x)-containinggas stream is generated in the headspace above an acid pickling tank orbath that may include, for example, nitric acid, and in which an alloyis immersed (i.e., “pickled”) for a time to treat the alloy's surfaces.In certain other non-limiting embodiments, the NO_(x)-containing gasstream is generated by a spray pickling process in which a spray of anacid pickling solution is directed at surfaces of a metal or alloy. Incertain non-limiting embodiments, the NO_(x)-containing gas streamgenerated by an acid pickling process may have a temperature in therange of ambient temperature to 140° F. As is known in the art, the acidsolution used in an acid pickling tank, bath, or spray is a solutionthat includes one or more strong acids and which is used to removesurface impurities such as stains, inorganic contaminants, rust, andscale, from metals and metal alloys. In certain embodiments, thepickling tank, bath, or spray may be used to remove surface impuritiesfrom materials selected from titanium, titanium alloys, and stainlesssteels.

In certain non-limiting embodiments, the pickling bath may include oneor more strong acids selected from the group consisting of hydrochloricacid, sulfuric acid, phosphoric acid, nitric acid, hydrofluoric acid,and combinations thereof. In certain specific non-limiting embodiments,the pickling bath may include one or both of nitric acid andhydrofluoric acid. Person having ordinary skill in the art may readilyformulate a suitable pickling solution for a particular metal or alloyand, therefore, it is not necessary that the present description includea discussion of how to formulate or apply a pickling solution for aparticular metal or alloy. It will be understood that embodiments of themethod and system according to the present disclosure may be used withany pickling formulation that generates a NO_(x)-containing gas. Moregenerally, it will be understood that certain embodiments of the methodand system according to the present disclosure may be used to processNO_(x)-containing gas produced by any process, apparatus, system, orphenomenon.

In certain non-limiting embodiments of a method or system according tothe present disclosure used in connection with a pickling process, thepickling solution within a pickling tank or bath or used in a picklingspray may have a temperature of at least 140° F. However, it will beunderstood that the pickling solution may have any temperature suitablefor pickling a metal or alloy of interest. For example, in certainnon-limiting embodiments, the pickling solution may have a temperatureless than 140° F. In certain other non-limiting embodiments, thepickling solution may have a temperature equal to or higher than 140° F.In other non-limiting embodiments of a method or system according to thepresent disclosure used in connection with a pickling process, thepickling bath or tank may hold at least 5700 and as much as 15,000gallons of pickling solution. However, it will be understood that thepickling bath or tank may hold any volume of pickling solution suitablefor providing the desired surface processing of a metal or alloy millproduct of interest. As previously noted, in certain other non-limitingembodiments of a pickling process that generates NO_(x)-containing gas,surface impurities such as stains, inorganic contaminants, rust, andscale, may be removed from metals and alloys using spray pickling. Asused herein, spray pickling refers to a process of spraying an acidpickling solution on metal and/or metal alloy to remove surfaceimpurities. Spray pickling may minimize or reduce the volume of acidthat is used to treat the metal and/or metal alloy, but the process maystill produce significant volumes of NO_(x)-containing gas.

Again referring to the system 13 schematically illustrated in FIG. 2,the first inlet 4 may further communicate with a source of moisture(water). In certain non-limiting embodiments of system 13, the moistureand the NO_(x)-containing gas stream enter the first chamber 1 at thesame location, which may be, for example, inlet 4. In other non-limitingembodiments, the moisture and the NO_(x)-containing gas stream may enterthe first chamber 1 at different locations. In yet other non-limitingembodiments, all or a portion of the moisture introduced into the firstchamber 1 may be part of the NO_(x)-containing gas stream. For example,in embodiments of the method and system described herein associated witha pickling process or system, the NO_(x)-containing gas stream may begenerated in the headspace of the acid pickling solution and, therefore,may include a certain moisture content as a result of evaporation ofwater from the acid pickling solution.

The second inlet 5 to chamber 1 of the system 13 communicates with asource of ozone. The ozone source may be, for example, an ozonegenerator or another known device that produces ozone (not shown), or anozone storage device. In certain non-limiting embodiments, the ozonegenerating device may be located “on-site” so that ozone may be producedwhen needed to treat NO_(x)-containing gas generated by a picklingprocess or apparatus or another process or apparatus at the site.Because ozone has a short half-life, the ozone preferably is generatedproximate the second inlet 5. For example, in certain non-limitingembodiments, an ozone generator device or other ozone source may belocated near the second inlet 5. In other non-limiting embodiments, theozone source may be located near the first inlet 4 and the second inlet5. The ozone source may provide an ozone-containing gas stream includingozone in any concentration suitable to treat the particularNO_(x)-containing gas stream that is being introduced into the firstchamber 1. In certain non-limiting embodiments, the concentration ofozone in the gas stream introduced into the first chamber 1 at secondinlet 5 may be in the range of 1 to 16 percent by volume.

In certain non-limiting embodiments of system 13, the second inlet 5, atwhich a gas including ozone is introduced into the first chamber 1 maybe located adjacent (i.e., near to) the first inlet 4 so that NO_(x)entering the first chamber 1 at the first inlet 4 contacts ozoneintroduced at the second inlet 5 and suitably reacts to form oxidationproducts including nitrogen sesquioxide and nitrogen pentoxide. Thosehaving ordinary skill may readily ascertain a suitable minimum, maximum,and/or range of distances between the first inlet 4 and the second inlet5 so that the NO_(x) in the NO_(x)-containing gas stream and the ozonein the ozone-containing gas stream react within the first chamber 1 to adegree that results in the particular desired minimum reduction in theconcentration of NO_(x) in the NO_(x)-containing gas stream entering thefirst chamber 1. The shape and size of the interior volume of the firstchamber 1 may be adapted to promote contact between and thereby suitablyreact the NO_(x)-containing gas stream and the ozone to produceoxidation products including nitrogen sesquioxide and nitrogenpentoxide. These reaction products can be formed in the first chamber 1by reaction of nitrogen oxides (NO_(x), including NO_(x) and NO₂) andozone (O₃) according to the following equations:

NO+O₃→NO₂+O₂

NO₂+O₃→NO₃+O₂

NO₃+NO₂⇄N₂O₅   A.)

NO+NO₂⇄N₂O₃   B.)

The degree to which the NO_(x) in the NO_(x)-containing gas streamreacts with the ozone in the first chamber 1 to form oxidation productsincluding nitrogen sesquioxide and nitrogen pentoxide depends on manyfactors including, but not limited to, the flow rates of the gases,residence time, the concentration on NO_(x) and ozone in the respectivegas streams, the temperatures of the reactants, and the particularmixing action that occurs between the gas streams within the firstchamber 1. Those having ordinary skill may suitably adjust or influenceone or more of these parameters to adjust the reaction rate occurring inthe first chamber 1 and achieve the desired level of conversion ofNO_(x) in the NO_(x)-containing gas stream.

In certain non-limiting embodiments of the system 13, theNO_(x)-containing gas stream is not treated in a scrubber prior to beingintroduced into the interior volume of the first chamber 1 andcontacting ozone therein. Also, in certain non-limiting embodiments of asystem according to the present disclosure, the NO_(x)-containing gasstream may be mixed with the ozone-containing gas stream in the firstchamber using a device adapted to mix gas streams. For example, theNO_(x)-containing gas stream may be mixed with ozone-containing gasstream using a static mixer. As used herein, the term “static mixer”refers to a device that includes a series of fixed elements with aspecific geometric design so as to promote patterns of flow division andradial mixing. A static mixer may be used to promote mixing of at leasttwo liquids or at least two gases, to disperse a gas into a liquid, orto disperse at least two immiscible liquids. Although it is believedthat a static mixer is not required in the system 13, providing a staticmixer may improve system efficiency and reduce the length of the firstchamber 1 necessary to allow the gas streams introduced into the firstchamber 1 to mix and suitably react. In certain non-limiting embodimentsof the system 13, for example, a static mixer may be located in orassociated with the first chamber 1 near the first inlet 4 and thesecond inlet 5. In certain non-limiting embodiments of system 13, astatic mixer may be located immediately following the second inlet 5.

At least a portion of the nitrogen sesquioxide and nitrogen pentoxideoxidation products formed in the first chamber 1 further react withwater in the interior volume of the first chamber 1 to form nitric acid.As discussed above, water introduced into the interior volume of thefirst chamber 1 may be, for example, moisture that is already acomponent of the NO_(x)-containing gas stream introduced into the firstchamber 1 at first inlet 4 and/or water introduced into the firstchamber 1 from one or more inlets into the first chamber 1 thatcommunicate with one or more water sources. A possible water source 6 isindicated in FIG. 2. It will be understood that the system 13 may beconstructed in any suitable way so that a sufficient concentration ofwater is present in the first chamber 1 to suitably react with oxidationproducts in the first chamber and form nitric acid. In certainnon-limiting embodiments, the first inlet 4 may be located near thewater source 6. In certain other non-limiting embodiments, the firstinlet 4 and second inlet 5 may be located near the water source 6. Itwill be understood that the particular design of the system 13 and thefirst chamber 1 will influence the optimal positioning of the one ormore water inlets into the first chamber 1, if such is provided, so asto optimally facilitate reaction of water and oxidation products in thefirst chamber 1.

Again referring to FIG. 2, the second chamber 2 of system 13 may belocated downstream (i.e., in the direction of gas flow) from the firstchamber 1. The first and second chambers 1,2 preferably are directlyfluidly connected so that the effluent from the first chamber 1 flows tothe second chamber 2. The second chamber is adapted to recover nitricacid from the effluent emerging into the second chamber 2 from the firstchamber 1. In certain embodiments of the system 13, the second chamber 2may be a mist eliminator which, as is known to those having ordinaryskill, is a device including a large cross-sectional surface areaadapted for condensation of liquid from a mist introduced (e.g.,injected) into the mist eliminator. A mist eliminator preferably removesmist as a liquid from a gas stream by reducing the velocity of gas as itpasses through the mist eliminator, thereby trapping the mist so that itmay be removed as a liquid via gravity.

As illustrated in FIG. 2, in certain non-limiting embodiments, thesecond chamber 2 of system 13 may include a third inlet 7, an interiorvolume, and an outlet 8 through which solubilized nitric acid iscollected or recovered from the interior volume. The third inlet 7communicates with a source of water vapor which, in certain non-limitingembodiments, is sprayed into the interior volume of the second chamber2. The interior volume is adapted to contact gaseous effluent from thefirst chamber 1 with water vapor to thereby solubilize in the watervapor nitric acid in the gaseous effluent from the first chamber 1. Thesolubilized nitric acid is then collected as an aqueous nitric acidsolution and is extracted from the bottom of the second chamber 2through outlet 8. The concentration of the nitric acid may be adjustedby, for example, controlling the volume of water that is introduced intothe system 13 over time. For example, introducing water into the system13 at a relatively high rate, as a component of the NO_(x)-containinggas stream and/or through one or more water inlets associated with thefirst chamber 1, may dilute the nitric acid formed in and recovered fromthe system 13. Alternatively, introducing a lesser volume of water inthe system 13 over time may concentrate the nitric acid formed in andrecovered from the system 13.

In certain embodiments, the recovered nitric acid is recycled back tothe process or apparatus that initially generated the NO_(x)-containinggas that is treated by the system 13. For example, in the embodiment inwhich the system 13 is associated with a pickling tank, bath, or spraythat produces an NO_(x)-containing gas stream treated in the system 13,the nitric acid recovered from the second chamber 2 may be piped orotherwise transferred back to the pickling tank, bath, or spray and usedto pickle additional metal or alloy mill products. Alternatively, thenitric acid recovered from the second chamber 2 may be stored, sold, orproperly disposed of, for example.

Again referring to FIG. 2, system 13 optionally includes a third chamber3 that is located downstream from the second chamber 2 and receives thegaseous effluent from chamber 2. In certain non-limiting embodiments,the third chamber 3 may be a scrubber. A scrubber is a device or systemthat extracts pollutants or other materials from a gas stream. As isknown in the art, a scrubber may be a wet scrubber, which uses a liquidto remove materials from a gas stream, or a dry scrubber, which uses adry material to remove materials from a gas stream. For example, thegaseous effluent from chamber 2 may include un-reacted nitrogen oxides,nitric acid that has not been captured by the second chamber 2, nitricacid produced in regions of the system 13 beyond the second chamber 2,mercury, sulfur oxides, and/or entrained particulates that one wishes toremove from the gas stream exiting the second chamber 2, and suchmaterials may be fully or partially removed using a scrubber in thethird chamber 3. For example, nitrogen oxides that are not converted tooxidation products in the first chamber 1 may pass un-reacted throughthe second chamber 2 and enter the third chamber 3. Such un-reactednitrogen oxides may be partially or fully removed from the gas stream inchamber 3. Also, for example, nitric acid that is not recovered in thesecond chamber 2 may enter the third chamber 3 through conduit 9 and bepartially or wholly collected in the third chamber 3.

In certain non-limiting embodiments, the third chamber 3 may include afourth inlet 10, a terminal outlet 12 for releasing a gas to theenvironment, and a second outlet 11 for collecting waste from theinterior volume of the third chamber 3. In embodiments in which thethird chamber 3 is a wet scrubber device, the fourth inlet 10 maycommunicate with a source of a scrubber solution. The scrubber solutionmay be, for example, a non-caustic solution, such as water, or a causticsolution, such as a water/sodium hydroxide solution. In certainnon-limiting embodiments, the particular scrubber solution may berecirculated through the scrubber to neutralize non-recovered nitricacid passing into the third chamber 3. The first outlet 12 releases anynitrogen oxides (NO_(x)) that are not removed in the second chamber 2 orthird chamber 3. The second outlet 11 may be used for extracting wastesfrom the third chamber 3, and the waste may be reused and/or disposedof, as the case may be.

A NO_(x)-containing gas stream treatment system constructed as generallydescribed in the present disclosure can produce a significant volume ofnitric acid in a 24 hour period. For example, it is believed that anapparatus constructed as generally shown in FIG. 2 could potentiallyrecover as much as 1350 pounds/day of nitric acid (based on 100% acid)from a waste gas stream including 1200 ppm NOx and flowing at a rate of4,500 scfm (standard cubic feet per minute). Tests conducted on aprototype system constructed as generally discussed according to thepresent disclosure and having the general design shown in FIG. 2successfully produced a significant volume of 42% (volume/volume) nitricacid from a NOx-containing gas stream produced by an alloy picklingapparatus.

This disclosure has been written with reference to various exemplary,illustrative, and non-limiting embodiments. However, it will berecognized by persons having ordinary skill in the art that varioussubstitutions, modifications, or combinations of any of the disclosedembodiments (or portions thereof) may be made without departing from thescope of the invention. Thus, it is contemplated and understood that thepresent disclosure embraces additional embodiments not expressly setforth herein. Such embodiments may be obtained, for example, bycombining, modifying, or reorganizing any of the disclosed steps,components, elements, features, aspects, characteristics, limitations,and the like, of the embodiments described herein. In this regard,Applicant reserves the right to amend the claims during prosecution toadd features as variously described herein.

1. A system for treating a gas stream comprising NOx generated from anacid pickling solution, the system comprising: a first chamber includinga first inlet communicating with a source of a gas comprising NOxgenerated by an acid pickling solution in an acid pickling tank, acidpickling bath, or acid pickling spray, a second inlet communicating witha source of ozone, and an interior volume adapted to contact the gascomprising NOx introduced through the first inlet with the ozoneintroduced through the second inlet, thereby producing oxidationproducts including nitrogen sesquioxide and nitrogen pentoxide, whereinat least a portion of the nitrogen sesquioxide and nitrogen pentoxidereact with water in the first chamber to form nitric acid; and a secondchamber directly fluidly communicating with the first chamber andreceiving gaseous effluent comprising nitric acid from the firstchamber, the second chamber including a third inlet communicating with asource of water vapor, an interior volume adapted to contact the gaseouseffluent from the first chamber with the water vapor introduced throughthe third inlet, thereby solubilizing nitric acid in the gaseouseffluent with the water vapor to provide a solubilized nitric acid, andan outlet for collecting solubilized nitric acid from the interiorvolume of the second chamber, wherein the outlet fluidly communicateswith the acid pickling tank, acid pickling bath, or acid pickling spray,whereby at least a portion of the solubilized nitric acid collectedthrough the outlet is delivered to the acid pickling tank, acid picklingbath, or acid pickling spray.
 2. The system of claim 1, wherein the acidpickling tank, acid pickling bath, or acid pickling spray includes anacid pickling solution comprising nitric acid.
 3. The system of claim 1,wherein the acid pickling tank, acid pickling bath, or acid picklingspray is used to treat surfaces of materials selected from metals andalloys.
 4. The system of claim 1, wherein the acid pickling tank, acidpickling bath, or acid pickling spray is adapted to treat surfaces ofmaterials selected from stainless steel, titanium, and titanium alloys.5. The system of claim 1, wherein the first chamber includes a staticmixer adapted to mix the gas stream comprising NOx and the ozone in theinterior volume of the first chamber.
 6. The system of claim 1, whereinthe first chamber further comprises a third inlet that communicates witha source of water vapor.
 7. The system of claim 1, wherein the source ofozone is an ozone generator.
 8. The system of claim 1, wherein thesecond inlet is located adjacent the first inlet.
 9. The system of claim1, wherein a diameter of the first chamber is at least 24 inches. 10.The system of claim 1, wherein the second chamber is a mist eliminator.11. A system for treating a gas stream comprising NOx generated from anacid pickling solution, the system comprising: a first chamber includinga first inlet communicating with a source of a gas comprising NOxgenerated by an acid pickling solution in an acid pickling tank, acidpickling bath, or acid pickling spray, a second inlet communicating withan ozone generator, a third inlet communicating with a source of watervapor, and an interior volume comprising a static mixer adapted to mixthe mix the gas comprising NOx introduced through the first inlet withthe ozone introduced through the second inlet in the interior volume ofthe first chamber, thereby producing oxidation products includingnitrogen sesquioxide and nitrogen pentoxide, wherein at least a portionof the nitrogen sesquioxide and nitrogen pentoxide react with water inthe first chamber to form nitric acid; and a second chamber directlyfluidly communicating with the first chamber and receiving gaseouseffluent comprising nitric acid from the first chamber, the secondchamber including a third inlet communicating with a source of watervapor, an interior volume adapted to contact the gaseous effluent fromthe first chamber with the water vapor introduced through the thirdinlet, thereby solubilizing nitric acid in the gaseous effluent with thewater vapor to provide a solubilized nitric acid, and an outlet forcollecting solubilized nitric acid from the interior volume of thesecond chamber, wherein the outlet fluidly communicates with the acidpickling tank, acid pickling bath, or acid pickling spray, whereby atleast a portion of the solubilized nitric acid collected through theoutlet is delivered to the acid pickling tank, acid pickling bath, oracid pickling spray.
 12. The system of claim 11, wherein the acidpickling tank, acid pickling bath, or acid pickling spray includes anacid pickling solution comprising nitric acid.
 13. The system of claim11, wherein the acid pickling tank, acid pickling bath, or acid picklingspray is used to treat surfaces of materials selected from metals andalloys.
 14. The system of claim 11, wherein the acid pickling tank, acidpickling bath, or acid pickling spray is adapted to treat surfaces ofmaterials selected from stainless steel, titanium, and titanium alloys.15. A system for treating surfaces of materials selected from metals andalloys, the system comprising: a pickling apparatus comprising at leastone of an acid pickling tank, acid pickling bath, and acid picklingspray; a first chamber including a first inlet communicating with asource of a gas comprising NOx generated by acid pickling solution inthe acid pickling tank, acid pickling bath, or acid pickling spray, asecond inlet communicating with a source of ozone, and an interiorvolume adapted to contact the gas comprising NOx introduced through thefirst inlet with the ozone introduced through the second inlet, therebyproducing oxidation products including nitrogen sesquioxide and nitrogenpentoxide, wherein at least a portion of the nitrogen sesquioxide andnitrogen pentoxide react with water in the first chamber to form nitricacid; and a second chamber directly fluidly communicating with the firstchamber and receiving gaseous effluent comprising nitric acid from thefirst chamber, the second chamber including a third inlet communicatingwith a source of water vapor, an interior volume adapted to contact thegaseous effluent from the first chamber with the water vapor introducedthrough the third inlet, thereby solubilizing nitric acid in the gaseouseffluent with the water vapor to provide a solubilized nitric acid, andan outlet for collecting solubilized nitric acid from the interiorvolume of the second chamber, wherein the outlet fluidly communicateswith the acid pickling tank, acid pickling bath, or acid pickling spray,whereby at least a portion of the solubilized nitric acid collectedthrough the outlet is delivered to the acid pickling tank, acid picklingbath, or acid pickling spray.
 16. The system of claim 1, wherein thepickling apparatus includes an acid pickling solution comprising nitricacid.
 17. The system of claim 15, wherein the materials treated in thesystem are selected from stainless steel, titanium, and titanium alloys.18. The system of claim 15, wherein the first chamber includes a staticmixer adapted to mix the gas stream comprising NOx and the ozone in theinterior volume of the first chamber.
 19. The system of claim 15,wherein the first chamber further comprises a third inlet thatcommunicates with a source of water vapor.
 20. The system of claim 15,wherein the source of ozone is an ozone generator.
 21. The system ofclaim 15, wherein the second inlet is located adjacent the first inlet.22. The system of claim 15, wherein a diameter of the first chamber isat least 24 inches.
 23. The system of claim 15, wherein the secondchamber is a mist eliminator.